The present invention relates to a detachable device intended to hold together a plurality of objects, such as metal sheets.
The present invention has been developed to deal with the following problem: when it is necessary to fasten two sheets together, for example by riveting, the sheets must first be laid one on the other in the appropriate relative position and clamped so as to hold them in this relative position during the fastening operations, which may comprise the piercing of a hole passing through the two sheets, placing a rivet in position in this hole, and the shaping of this rivet.
For this purpose holes are prepared in advance in each of the sheets which are to be fixed together, these holes having to come into line with one another when the sheets are in the correct position, and then, after the sheets have been brought together, provisional fastening devices, known as "pinning clips" or more simply "pins", are inserted into these holes, these devices having an expansible rod which can penetrate into the holes in the sheets and then be widened out therein to effect centering, while a sliding body, pressed with the interposition of a spring by a nut screwed onto the expansible rod, clamps the sheets one against the other with a controlled force.
The expansible rod conventionally consists of a metal tube, an end part of which is divided into a plurality of sectors by longitudinal slits, and of an expansion rod slidable inside the tube and having a widened head with a section larger than the inside section of the slit part of the tube but smaller than that of the holes. By pulling the expansion rod so as to cause the head to penetrate into the slit part of the tube the sectors of the latter, which are formed by the longitudinal slits, are opened out until they come to bear against the interior of a hole.
Pins in use at the present time are relatively complicated devices, and therefore relatively expensive. Moreover, when the sectors of the tube are opened out they may damage or deform the interior of the hole, particularly the edge at the end of the hole. In addition, they project over a relatively considerable length on one of the sheets which are to be fastened together, thus complicating the positioning of the tools required for the riveting and possibly hindering automatic work when these tools are carried by a robot arm.
In U.S. Pat. No. 4,936,726, J. MEDARD, a pin of a type similar to that described above has been proposed, in which the expansible rod comprises two elastic blades diametrically opposite in relation to an axis and carrying, at their ends, radially widened hooking members. By axially moving the elastic blades relative to a fixed axial cylindrical rod, the hooking members are displaced radially. Said members are surrounded by a protective tube of deformable material. This arrangement avoids the risk of damaging the interior of the hole, but is more complicated than that of the prior art because of the presence of the protective tube.
In U.S. Pat. No. 2,353,248, W. H. LAMB, a pin has also been proposed in which the tubular member is itself of elastically deformable material and is held axially by an end which bears against the body. The head has a plane radial surface which comes to bear against the other end of the tubular member, this end likewise consists of a plane radial surface. Movement of the head towards the body entails axial compression of the tubular member, and the latter is forced to widen out radially.
This device has a smaller number of components than the previous device, but this number is still fairly large. Furthermore, the radial deformation of the tubular member requires substantial forces. This has the consequence that the device must be stronger than those of the prior art, and this increases its cost. Moreover, the life of the tubular member, which is heavily stressed, is shortened.
The object of the present invention is to provide a pinning clip which is simpler and less expensive than those of the prior art, and which in addition cannot damage or deform the hole.
Another object of the invention is to provide a device of this kind which is less bulky than those currently in use.
Yet another object of the invention is to provide a device of this kind which is decidedly quicker to use than the devices currently in use.